[PATCH v4] powerpc/kdump: Add support for crashkernel CMA reservation

[Sourabh Jain]

Hi Ritesh,

On 31/10/25 09:27, Ritesh Harjani (IBM) wrote:
> Sourabh Jain <sourabhjain at linux.ibm.com> writes:
>
>> Commit 35c18f2933c5 ("Add a new optional ",cma" suffix to the
>> crashkernel= command line option") and commit ab475510e042 ("kdump:
>> implement reserve_crashkernel_cma") added CMA support for kdump
>> crashkernel reservation.
>>
>> Extend crashkernel CMA reservation support to powerpc.
>>
>> The following changes are made to enable CMA reservation on powerpc:
>>
>> - Parse and obtain the CMA reservation size along with other crashkernel
>>    parameters
>> - Call reserve_crashkernel_cma() to allocate the CMA region for kdump
>> - Include the CMA-reserved ranges in the usable memory ranges for the
>>    kdump kernel to use.
>> - Exclude the CMA-reserved ranges from the crash kernel memory to
>>    prevent them from being exported through /proc/vmcore.
>>
>> With the introduction of the CMA crashkernel regions,
>> crash_exclude_mem_range() needs to be called multiple times to exclude
>> both crashk_res and crashk_cma_ranges from the crash memory ranges. To
>> avoid repetitive logic for validating mem_ranges size and handling
>> reallocation when required, this functionality is moved to a new wrapper
>> function crash_exclude_mem_range_guarded().
>>
>> To ensure proper CMA reservation, reserve_crashkernel_cma() is called
>> after pageblock_order is initialized.
>>
>> Cc: Baoquan he <bhe at redhat.com>
>> Cc: Jiri Bohac <jbohac at suse.cz>
>> Cc: Hari Bathini <hbathini at linux.ibm.com>
>> Cc: Madhavan Srinivasan <maddy at linux.ibm.com>
>> Cc: Mahesh Salgaonkar <mahesh at linux.ibm.com>
>> Cc: Michael Ellerman <mpe at ellerman.id.au>
>> Cc: Ritesh Harjani (IBM) <ritesh.list at gmail.com>
>> Cc: Shivang Upadhyay <shivangu at linux.ibm.com>
>> Cc: linuxppc-dev at lists.ozlabs.org
>> Signed-off-by: Sourabh Jain <sourabhjain at linux.ibm.com>
>> ---
>> Changlog:
>>
>> v3 -> v4
>>   - Removed repeated initialization to tmem in
>>     crash_exclude_mem_range_guarded()
>>   - Call crash_exclude_mem_range() with right crashk ranges
>>
>> ---
>>   arch/powerpc/include/asm/kexec.h   |  2 ++
>>   arch/powerpc/kernel/setup-common.c |  4 ++-
>>   arch/powerpc/kexec/core.c          | 10 ++++++-
>>   arch/powerpc/kexec/ranges.c        | 43 ++++++++++++++++++++++--------
>>   4 files changed, 46 insertions(+), 13 deletions(-)
>
> I am not much familiar with the crash kernel workings but was curious
> about the following query related to this patch:
>
> As I understand this patch allows for the remaining crash kernel
> memory to come from CMA region. But do we limit the CMA region to be lower
> than 4G?

No we are not and we don't need to.

> Is this patch dependent over your other patch series [1] which
> supports high crashkernel reservation?
>
> [1]: https://lore.kernel.org/linuxppc-dev/20251027151338.819957-1-sourabhjain@linux.ibm.com/

No, this is an independent patch.

>
>
> A minor comment: I guess we could reflect the support for ,cma for PPC
> too in Documentation/admin-guide/kernel-parameters.txt like how it is
> done for x86.

Yes we should. I will make the change in the next version.

Thanks for the review.

- Sourabh Jain